Idling system for power hammer

ABSTRACT

An electric paving breaker is described which includes an electric motor, a crank and piston driven by the motor, and a ram driven by the piston which delivers energy to a tool bit to produce a hammering output. An improved idling system to prevent the piston from driving the ram unless a tool bit is in place is described.

United States Patent Sides et a1.

1451 Sept. 17, 1974 [541 IDLING SYSTEM FOR POWER HAMMER 3.568780 3/1971Matsuo 173 116 [75] In e o Da e arrison S des, Ne 3,650,336 3/1972Koehler 173/116 Freedom, Pa.; Robert Gordon FOREIGN PATENTS ORAPPLICATIONS Mom, cockeysvlue 714,864 9 1954 Great Britain 173 116 [73]Assignee: The Black and Decker Manufacturing Company, Towson, PrimaryExaminer-Frank L. Abbott Md. Assistant Examiner-William F. Pate, IllAttorney, Agent, or FirmEdward D. Murphy; [22] Ffled' 1973 LeonardBloom; Joseph R. Slotnik [21] Appl. No.: 342,865

[57] ABSTRACT 2% g 5 1 3 An electric paving breaker is described whichincludes 'i 116 122 13 an electric motor, a crank and piston driven bythe l 1 3 Z7; "66 1 motor, and a ram driven by the piston which deliversenergy to a tool bit to produce a hammering output. An improved idlingsystem to prevent the piston from [56] References Clted driving the ramunless a tool bit is in place is de- UNITED STATES PATENTS Scribe1,424,188 8/1922 Smith 173/138 3,507,337 4 1970 Chromy 173 14 11 Clam, 5Dmwmg Flgures Ar /1 I// 1 IDLING SYSTEM FOR POWER HAMMER The presentinvention is directed to heavy-duty power tools of the type used aspaving breakers and for other demolition work, and is specificallydirected to an improved idling system for power hammer tools.

The tools to which this invention relates are those which generallyinclude a source of power such as an air or electric motor, a pistonconnected to and driven by the power source and a ram element which isdisposed between the piston and an output device. As the piston isreciprocated by the power source, energy is delivered from the piston tothe ram and, as the ram reciprocates, it encounters an output means suchas a chisel bit and energy is delivered to a workpiece such as pavementor concrete, etc. In the course of using such hammers, the operatorscommonly turn the switch controlling the power source on and hold it onas they apply the tool to various locations on the workpiece. When thetool is in contact with the workpiece, the bit, which is slidablymounted in the front end of the tool, is held in position to receive thefull energy of the ram. However, as the tool is lifted and transferredto a new location, the bit slides partially out of the tool untilstopped by a bit retainer. In this position, if the ram continues to bedriven by the piston, the energy will no longer be taken by theworkpiece, but will be applied to the front end of the tool itself. Thiseither requires unnecessary structural strength in the front end of thetool or else the tool may be subject to premature failure.

To avoid this difficulty, it is desirable to provide an arrangementwhich will prevent the ram from reciprocating unless the tool bit is inposition in the front of the tool and is held in its fully inwardposition by a workpiece. Ram catchers and rubber beat pieces which havepreviously been used are quickly mashed and ruined in large tools; aircushion devices have not provided adequate protection against hammeringduring idling. It is, therefore, the purpose of the present invention toprovide an idling system, particularly for large power hammers, whichwill prevent the ram from reciprocating when the tool bit is not inproper position and which will not interfere with the normal operationof the tool when the bit is in its proper position relative to the ram.

Accordingly, it is an object of the present invention to provide a newand improved idling system for power hammer tools.

A further object of this invention is the provision of a new andimproved hammer idling means which is more effective and more reliablethan previous arrangements.

Further objects and advantages of this invention will become apparent asthe description and illustration thereof proceed.

Briefly, in accord with one embodiment of this invention, a powerhammer, specifically a paving breaker, is disclosed which includes anelectric motor as a source of power, a gearing system for reciprocatinga piston upon rotation of the motor, and a ram which is arranged to becoupled to and driven by the piston when the tool is in use. Means areprovided for mounting and retaining an output bit which is driven by theram when the tool is held against a workpiece. In specific accord withthe present invention, an enclosed chamber having a check valve isprovided at the bottom of the ram cylinder. In normal operation, the bitprotrudes into this region, thuspreventing the ram from reaching thebottom of the chamber. When the bit is removed from the tool, or whenthe tool is lifted from a workpiece so that the bit slides forwardly outof the normal range of the ram, the next power stroke of the ramcompresses air in the chamber, slowing the ram and then opening thecheck valve so that the ram travels to the end of the cylinder. Meansare provided to interrupt the normal coupling between the piston and theram when the ram is at the bottom of the cylinder so that the ramremains stationary despite continued reciprocation of the piston. Theram remains in this position until it is lifted away from the bottom ofthe chamber by means of a tool bit being forced against a workpiece.This moves the ram upwardly in the cylinder to re-establish couplingbetween the piston and the ram and normal operation of the tool resumes.

In the drawing:

FIG. 1 is an elevational view of an electric paving breaker whichembodies an idling system in accord with the present invention;

FIG. 2 is a schematic cross-sectional view through the tool of FIG. 1which shows the internal mechanism of the tool;

FIG. 3 is a cross-sectional view of the forward end of the pavingbreaker of FIG. 1, which illustrates an idling system in accord withthis invention;

FIG. 4 is a cross-sectional view corresponding to FIG. 2 but showing theparts at another point in the operation; and

FIG. 5 is a cross-sectional view similar to that of FIG. 2 but showingan alternative embodiment of this invention.

FIG. 1 illustrates generally an electric paving breaker in accord withthe present invention. The tool, indicated generally at 1, includes amotor housing 2, a transmission housing 3, and a barrel 4. An outputmember such as a chisel bit 5 is retained on the paving breaker by meansof a tool bit retainer 6.

The internal mechanism of this particular tool is shown in schematicform in FIG. 2 wherein it can be seen that this specific embodiment usesan electric motor 7 which drives a crank 8 by means of shaft pinion 9,right angle gear 10, spur pinion 11 and crank gear 12. All of theseelements are, of course, supported in suitable bearings and lubricatedas required. The crank 8 includes a journal portion 13 which supportsthe upper end 14 of a connecting rod 15. The connect ing rod is coupledin a conventional manner to a piston 16 which reciprocates in the upperend of the barrel 4 upon rotation of the crank 8. At least one pistonring 17 is provided to seal the gap between the piston and the internalsurface 18 of the barrel so that an air spring is created in the region19. The air spring couples the reciprocation of the piston to a ram 20,causing it to be drawn up and then driven downwardly, producing a seriesof impacts on the bit 5 via a beat piece 21.

FIG. 3 illustrates the lower, or forward, end of the barrel 4. Withinthe barrel, the ram 20 is shown in its lowest position during workingoperation. In this position, the ram has just struck the beat piece 21which transmits the energy directly to the upper end 22 of the bit 5. Aspreviously described, this hammer makes use of the compression andexpansion of the volume of air contained in the region 19 between theram 20 and the piston. This air volume functions as a spring whichpermits the relatively slowly developing energy of the piston to betransferred rapidly to the ram, producing a high impact force, and whichalso isolates the motor and gear train from the shock loads when the ramimpacts the beat piece. To allow this action to occur, a plurality ofslots 23 are provided in the side of the barrel which communicate withthe atmosphere and which thus prevent the development of high pressureor a vacuum ahead of the ram.

In normal operation, when the tool bit is pressed against a workpiece,the forwardmost position of the ram is that shown in FIG. 3. In thisposition, the region 19 between the ram and the piston is still sealedfrom the exhaust slots 23; thus, the upward motion of the piston reducesthe pressure within chamber 19 and, in combination with the reboundenergy, causes movement of the ram away from the beat piece. It is alsonoted that, in normal operation, the ram is stopped by the beat piecejust as it enters a chamber 25 at the forward end of barrel 4. Thus, airtrapped within the chamber 25 does not affect the normal operation.

In front of the barrel 4, a nose piece 26 is provided to guide the toolbit 5. The nose piece is retained by a pair of roll pins, one of whichis shown at 27 and by a series of bolts 28. The bolts are threaded intoa retaining sleeve 29 which in turn is held within the barrel 4 by aretaining ring 30. The beat piece 21 includes a shoulder 31 which istrapped between internal shoulders 32 and 33 on the nose piece andretaining sleeve, respectively.

The retaining sleeve also includes a passageway 34 which communicateswith the chamber 25 and which is closed by a check valve 35, the checkvalve being held closed by a spring 36. When the check valve is opened,the passage 34 communicates to the atmosphere through holes 37 and 38,in the retaining sleeve and barrel, respectively. This system permitsthe ram to idle under certain conditions as will now be set forth inconjunction with a description of FIG. 4.

In FIG. 4, the mechanism is shown with the tool bit 5 removed and withthe beat piece 21 resting against the shoulder 32 of the nose piece.This illustrates the conditions which would apply if the tool wasoperated with the bit 5 removed or with the tool lifted away from theworkpiece so that the bit drops to the lowest position permitted by theretainer 6. In either of these cases, the first power stroke of thepiston drives the ram to and beyond the point at which it would normallyencounter the beat piece 21. As the ram enters the chamber 25, air istrapped within this chamber by virtue of the close fit of the ram withinbarrel 4. Thus, the pressure within chamber 25 rapidly increases,slowing and stopping the ram. At some predetermined level of pressure,determined by the spring 36, the check valve 35 opens as shown in FIG.4. This releases the air trapped in chamber 25 to atmosphere. Thedeceleration of the ram continues as excess pressure is relieved untilfinally the ram is stopped and the pressure in chamber 25 decreases toallow the valve 35 to close. At this point, the ram is below its normaloperational position in the barrel 4 and the chamber 19 between the ramand the piston is now exposed to atmospheric pressure via the upper endof the slots 23. Thus, as the piston starts its next upward stroke thesuction normally produced in chamber 19 simply draws air in from theatmosphere and no lifting force is applied to the ram. Since the ramreceives essentially no rebound energy from the air in chamber 25 andsince no lifting force is produced by the piston, the ram will remain atthe bottom of the barrel 4 as the piston continues to reciprocate.Therefore, after the first, controlled motion of the ram to the front ofthe tool, the ram remains stationary and the front of the tool is notsubjected to a continuing series of impacts which might produce seriousdamage.

When it is desired to resume normal operation, a tool bit must be inplace within the nose piece 26. Biasing the bit against a workpieceforces the beat piece 21 into the chamber 25 and lifts the ram until itagain closes the slots 23 from communication with chamber 19, thuspermitting suction in chamber 19 to draw the ram upwardly and normaloperation follows. In most cases, this tool is used in a verticalposition with the bit pointed down; the weight of the tool exertssufficient force on the bit to move the ram up out of the chamber 25.

FIG. 5 shows an alternative embodiment of this invention wherein thecheck valve 35 is replaced by a simple flapper valve 45. One end of theflapper valve is trapped between the nose piece 26 and the retainingsleeve 29 and a chamber 46 is provided in the nose piece to permit thevalve to open. This embodiment operates in a manner identical to thatdescribed with regard to FIG. 4.

In the foregoing description and drawings, two specific embodiments ofthis invention have been illustrated and described. However, it will beclear to those skilled in the art that many changes and modificationscan be made from these illustrations without departing from theessential teachings thereof. Accordingly, it is intended that theappended claims cover all such changes and modifications as may fallwithin the true spirit and scope of this invention.

We claim:

1. In a portable, power-operated impact tool of the type including acylinder; 21 power-driven piston arranged to reciprocate in one end ofsaid cylinder; a ram in said cylinder between said piston and the otherend of said cylinder; a normally sealed air volume between said pistonand said ram providing an air spring drive for said ram; at least oneopening in said cylinder normally communicating the region in front ofsaid ram to atmosphere; and means for slidably receiving a bit in saidother end of said cylinder for receiving impacts from said ram; theimprovement comprising a substantially closed chamber at said other endof said cylinder; said ram being prevented from entering said chamberwhen a bit is fully seated in said cylinder; a normally closed checkvalve in said chamber; said valve being set to open when air pressure insaid closed chamber exceeds a predetermined level to to dissipate thekinetic energy of said ram through said check valve and limit thevelocity of said ram as it traverses said chamber, and biasing meansclosing said valve as soon as said ram reverses its direction ofmovement to prevent said ram from rebounding out of said chamber.

2. An impact tool as claimed in claim 1 wherein a beat piece is providedat said other end of said cylinder for receiving blows from said ram andtransmitting them to a bit seated therein.

3. An impact tool as claimed in claim 2 wherein said beat piece isarranged to extend into said closed chamber when a bit is seated in saidcylinder, said beat piece being movable to a position out of saidchamber.

4. An impact tool as claimed in claim 3 wherein said check valve isarranged to communicate said chamber to atmosphere upon buildup of apredetermined pres sure in said chamber, whereby pressure in saidchambers prevents said ram from striking the bottom of said chamber at ahigh velocity.

5. In a portable, power-operated impact tool of the type including acylinder; a power-driven piston arranged to reciprocate in one end ofsaid cylinder; a ram in said cylinder between said piston and the otherend of said cylinder; a normally sealed air volume between said pistonand said ram providing an air spring drive for said ram; at least, oneopening in said cylinder normally communicating the region in front ofsaid ram to atmosphere; and means for slidably receiving a bit in saidother end of said cylinder for receiving impacts from said ram; theimprovement comprising a substantially closed chamber at said other endof said cylinder; said ram being prevented from entering said chamberwhen a bit is fully seated in said cylinder; a normally closed checkvalve in said chamber; said valve being arranged to open when airpressure in said closed chamber exceeds a predetermined level to limitmovement of said ram into said chamber, said valve being furtherarranged to close when the air pressure in said closed chamber isreduced to prevent said ram from rebounding out of said chamber; saidregion between said piston and said ram being communicated to atmospherewhen said ram is in said chamber so that said ram is lifted by saidpiston only when a bit is seated in said cylinder.

6. An impact tool as claimed in claim 5 wherein a beat piece is providedat said other end of said cylinder for receiving blows from said ram andtransmitting them to a bit seated therein.

7. An impact tool as claimed in claim 6 wherein said beat piece includesa portion extending into said closed chamber when a bit is seated insaid cylinder, said portion being movable to a position out of saidchamber.

8. An impact tool as claimed in claim 7 wherein said at least oneopening is blocked from communication with said air volume by said ramwhen said beat piece is moved into said chamber by a seated bit.

9. In a portable, power-operated impact tool of the type including adriving motor, a transmission driven by said motor, a cylinder, a pistonreciprocated in said cylinder by said transmission, a ram in saidcylinder and coupled to said piston by a normally sealed air volumetherebetween, a bit slidably disposed in the end of said cylinder forreceiving impacts from said ram when said bit is fully seated in the endof said cylinder, and at least one opening in said cylinder forcommunicating the region in front of said ram to atmosphere, theimprovement comprising a substantially closed chamber at the bit end ofsaid cylinder; said bit, in its fully seated position, preventing saidram from entering said chamber; a check valve in the opposite side ofsaid chamber from said ram, said check valve being positioned to openwhen said ram is driven into said chamber when said bit is not fullyseated in said cylinder whereby said ram is prevented from striking theend of said cylinder at a high velocity by air pressure in said chamber.

10. In a portable power-operated impact tool of the type including adriving motor, a transmission driven by said motor, a cylinder, a pistonreciprocated in said cylinder by said transmission, a ram in saidcylinder and coupled to said piston by a normally sealed air volumetherebetween, a bit slidably disposed in the end of said cylinder forreceiving impacts from said ram when said bit is fully seated in the endof said cylinder, and at least one opening in said cylinder forcommunicating the region in front of said ram to atmosphere; theimprovement comprising a substantially closed chamber at the bit end ofsaid cylinder; said bit, in its fully seated position, preventing saidram from entering said chamber; a check valve in the opposite side ofsaid chamber from said ram, said check valve being positioned to openwhen said ram is driven into said chamber when said bit is not fullyseated in said cylinder whereby said ram is prevented from striking theend of said cylinder at a high velocity by air pressure in said chamber;said opening in said cylinder being positioned to communicate with saidregion between said piston and said ram only when said ram is in saidchamber to prevent said ram from being reciprocated by said piston untilsaid bit lifts said ram out of said chamber.

11. A portable, power-operated, heavy-duty impact tool of the pavingbreaker type comprising a cylinder; a power-driven piston arranged toreciprocate in one end of said cylinder; a ram in said cylinder betweensaid piston and the other end of said cylinder; a normally sealed airvolume between said piston and said ram providing an air spring drivefor said ram; at least one opening in said cylinder normallycommunicating the region in front of said ram to atmosphere; and meansfor slidably receiving a bit in said other end of said cylinder forreceiving impacts from said ram; a substantially closed chamber at saidother end of said cylinder; said ram normally being prevented fromentering said chamber when a bit is fully seated in said cylinder; anormally closed check valve in said chamber; said valve being arrangedto open when air pressure in said closed chamber exceeds a predeterminedlevel; said region between said piston and said ram being communicatedto atmosphere when said ram is in said chamber; whereby operation ofsaid piston when a bit is fully seated in said chamber causesreciprocation of said ram; operation of said piston in the absence of abit and when a bit slides away from said chamber causing said ram toenter said chamber and remain in an idle mode.

1. In a portable, power-operated impact tool of the type including acylinder; a power-driven piston arranged to reciprocate in one end ofsaid cylinder; a ram in said cylinder between said piston and the otherend of said cylinder; a normally sealed air volume between said pistonand said ram providing an air spring drive for said ram; at least oneopening in said cylinder normally communicating the region in front ofsaid ram to atmosphere; and means for slidably receiving a bit in saidother end of said cylinder for receiving impacts from said ram; theimprovement comprising a substantially closed chamber at said other endof said cylinder; said ram being prevented from entering said chamberwhen a bit is fully seated in said cylinder; a normally closed checkvalve in said chamber; said valve being set to open when air pressure insaid closed chamber exceeds a predetermined level to to dissipate thekinetic energy of said ram through said check valve and limit thevelocity of said ram as it traverses said chamber, and biasing meansclosing said valve as soon as said ram reverses its direction ofmovement to prevent said ram from rebounding out of said chamber.
 2. Animpact tool as claimed in claim 1 wherein a beat piece is provided atsaid other end of said cylinder for receiving blows from said ram andtransmitting them to a bit seated therein.
 3. An impact tool as claimedin claim 2 wherein said beat piece is arranged to extend into saidclosed chamber when a bit is seated in said cylinder, said beat piecebeing movable to a position out of said chamber.
 4. An impact tool asclaimed in claim 3 wherein said check valve is arranged to communicatesaid chamber to atmosphere upon buildup of a predetermined pressure insaid chamber, whereby pressure in said chambers prevents said ram fromstriking the bottom of said chamber at a high velocity.
 5. In aportable, power-operated impact tool of the type including a cylinder; apower-driven piston arranged to reciprocate in one end of said cylinder;a ram in said cylinder between said piston and the other end of saidcylinder; a normally sealed air volume between said piston and said ramproviding an air spring drive for said ram; at least, one opening insaid cylinder normally communicating the region in front of said ram toatmosphere; and means for slidably receiving a bit in said other end ofsaid cylinder for receiving impacts from said ram; the improvementcomprising a substantially closed chamber at said other end of saidcylinder; said ram being prevented from entering said chamber when a bitis fully seated in said cylinder; a normally closed check valve in saidchamber; said valve being arranged to open when air pressure in saidclosed chamber exceeds a predetermined level to limit movement of saidram into said chamber, said valve being further arranged to close wHenthe air pressure in said closed chamber is reduced to prevent said ramfrom rebounding out of said chamber; said region between said piston andsaid ram being communicated to atmosphere when said ram is in saidchamber so that said ram is lifted by said piston only when a bit isseated in said cylinder.
 6. An impact tool as claimed in claim 5 whereina beat piece is provided at said other end of said cylinder forreceiving blows from said ram and transmitting them to a bit seatedtherein.
 7. An impact tool as claimed in claim 6 wherein said beat pieceincludes a portion extending into said closed chamber when a bit isseated in said cylinder, said portion being movable to a position out ofsaid chamber.
 8. An impact tool as claimed in claim 7 wherein said atleast one opening is blocked from communication with said air volume bysaid ram when said beat piece is moved into said chamber by a seatedbit.
 9. In a portable, power-operated impact tool of the type includinga driving motor, a transmission driven by said motor, a cylinder, apiston reciprocated in said cylinder by said transmission, a ram in saidcylinder and coupled to said piston by a normally sealed air volumetherebetween, a bit slidably disposed in the end of said cylinder forreceiving impacts from said ram when said bit is fully seated in the endof said cylinder, and at least one opening in said cylinder forcommunicating the region in front of said ram to atmosphere, theimprovement comprising a substantially closed chamber at the bit end ofsaid cylinder; said bit, in its fully seated position, preventing saidram from entering said chamber; a check valve in the opposite side ofsaid chamber from said ram, said check valve being positioned to openwhen said ram is driven into said chamber when said bit is not fullyseated in said cylinder whereby said ram is prevented from striking theend of said cylinder at a high velocity by air pressure in said chamber.10. In a portable power-operated impact tool of the type including adriving motor, a transmission driven by said motor, a cylinder, a pistonreciprocated in said cylinder by said transmission, a ram in saidcylinder and coupled to said piston by a normally sealed air volumetherebetween, a bit slidably disposed in the end of said cylinder forreceiving impacts from said ram when said bit is fully seated in the endof said cylinder, and at least one opening in said cylinder forcommunicating the region in front of said ram to atmosphere; theimprovement comprising a substantially closed chamber at the bit end ofsaid cylinder; said bit, in its fully seated position, preventing saidram from entering said chamber; a check valve in the opposite side ofsaid chamber from said ram, said check valve being positioned to openwhen said ram is driven into said chamber when said bit is not fullyseated in said cylinder whereby said ram is prevented from striking theend of said cylinder at a high velocity by air pressure in said chamber;said opening in said cylinder being positioned to communicate with saidregion between said piston and said ram only when said ram is in saidchamber to prevent said ram from being reciprocated by said piston untilsaid bit lifts said ram out of said chamber.
 11. A portable,power-operated, heavy-duty impact tool of the paving breaker typecomprising a cylinder; a power-driven piston arranged to reciprocate inone end of said cylinder; a ram in said cylinder between said piston andthe other end of said cylinder; a normally sealed air volume betweensaid piston and said ram providing an air spring drive for said ram; atleast one opening in said cylinder normally communicating the region infront of said ram to atmosphere; and means for slidably receiving a bitin said other end of said cylinder for receiving impacts from said ram;a substantially closed chamber at said other end of said cylinder; saidram normally being prevented from entering said chamber when a bit isfully seated in said cylinder; a normally cLosed check valve in saidchamber; said valve being arranged to open when air pressure in saidclosed chamber exceeds a predetermined level; said region between saidpiston and said ram being communicated to atmosphere when said ram is insaid chamber; whereby operation of said piston when a bit is fullyseated in said chamber causes reciprocation of said ram; operation ofsaid piston in the absence of a bit and when a bit slides away from saidchamber causing said ram to enter said chamber and remain in an idlemode.